Polymers of one or more alpha olefins are generally incompatible with polymers of one or more C.sub.8-10 vinyl aromatic monomers. As a result, it is difficult to blend or even laminate, for example, polystyrene and polyethylene. There have been a number of attempts to prepare copolymers of, for example styrene and ethylene. Such polymers could lead to two different developments. The copolymer might have the properties sought after in the blend or the copolymer may be a suitable compatibilizer so that the blend could be prepared.
U.S. Pat. No. 3,390,141 issued Jun. 25, 1968, assigned to the Shell Oil Company teaches a block copolymer of styrene and ethylene containing from 0.01 to 7 weight % of styrene block polymerized in the presence of a conventional Ziegler-Natta polymerization system. The patent teaches that the styrene is not incorporated into the ethylene backbone of the polymer but rather tends to be in styrene blocks at the end of the olefin homopolymer (Col. 2 lines 55-60).
U.S. Pat. No. 3,478,129 issued Nov. 11, 1969, assigned to Monsanto Company teaches a block polymer of styrene and ethylene. The polymer consists of blocks of crystallizable polystyrene blocks and blocks of polyethylene or atactic ethylene styrene copolymer. The polymerization process uses a conventional Ziegler-Natta catalyst and does not contemplate the process of the present invention.
U.S. Pat. No. 5,703,187 issued Dec. 30, 1997, assigned to the Dow Chemical Company teaches pseudo random co-polymers of styrene and ethylene. The patent teaches that the distinguishing feature of all pseudo random copolymers is the fact that all phenyl or bulky hindering groups substituted on the polymer backbone are separated by 2 or more methylene units. The polymers of the present invention are distinct over the polymers of the patent in that the polymers of the present invention comprise at least 10 weight % of the vinyl aromatic monomer in the form of one or more atactic pseudoblocks. Additionally the process for preparing such polymers uses a catalyst distinct from that disclosed in the reference.
WO 98/09999 filed by the Dow Chemical Company claims a different structure of an ethylene styrene copolymer. The reference teaches that the styrene in the styrene ethylene tetrad is inserted exclusively in the head to tail manner. The patent teaches away from blocks of more than two styrene monomer units.
There are a number of Idemitsu Kosan Co. Ltd. patents which teach polymers comprising blocks of syndiotactic polystyrene (the phenyl rings are alternating on opposite sides of the back bone) and the olefin is incorporated in repeating units (e.g. olefin blocks). The patent teaches blocks of syndiotactic polystyrene and does not suggest the atactic pseudoblock polystyrene of the present invention. Additionally, the process for preparing the block copolymers does not use the catalyst system contemplated by the present invention.
The present invention seeks to provide a polymer comprising one or more alpha olefins and one or more atactic pseudoblocks of polystyrene.